Fix unit tests on Python 3.11

[jstvz]

Adds 3.11 to feature test workflows and includes the following changes to get them to pass:

• Update enum assert for 3.11

  The behavior of string enums has changed in 3.11 what's new:

  Changed Enum.format() (the default for format(), str.format() and
  f-strings) of enums with mixed-in types (e.g. int, str) to also include
  the class name in the output, not just the member’s key. This matches
  the existing behavior of enum.Enum.str(), returning e.g.
  'AnEnum.MEMBER' for an enum AnEnum(str, Enum) instead of just 'MEMBER'.

• Update create_task_fixture for 3.11

  Python 3.11 removed pathlib._Accessor in bpo-43012: remove pathlib._Accessor python/cpython#25701. This
  broke our patch when it replaced a call to os.getcwd() with
  Path.cwd() in Path.absolute(). As a classmethod Path.cwd()
  receives the class as its implicit first argument meaning we can have 0
  or 1 arguments.

• Update mock.patch namespaces for 3.11

  Because class paths are used in Task definitions we go into import
  contortions to preserve them¹. 3.11 includes an update that replaces
  unittest.mock._importer with pkgutil.resolve_name, breaking
  mock.patch in several tests. For example:

  # Python 3.11.0 (main, Nov 29 2022, 08:46:07) [Clang 14.0.0 (clang-1400.0.29.202)] on darwin
  >>> clspth = "cumulusci.tasks.salesforce.Deploy.__call__"
  >>> import pkgutil
  >>> getter = lambda: pkgutil.resolve_name(clspth)
  >>> target = getter()
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "<stdin>", line 1, in <lambda>
    File "/Users/jestevez/.pyenv/versions/3.11.0/lib/python3.11/pkgutil.py", line 715, in resolve_name
      result = getattr(result, p)
               ^^^^^^^^^^^^^^^^^^
  AttributeError: module 'cumulusci.tasks.salesforce.Deploy' has no attribute '__call__'. Did you mean: '__file__'?
  >>> # However
  >>> from cumulusci.tasks.salesforce import Deploy
  >>> getattr(Deploy, '__call__')
  <function BaseTask.__call__ at 0x1113b7560>

  Updating our patches to point at the right namespace works for most of
  the mocks on 3.8+.

Footnotes

1. Read "contortions" as "I don't understand them." ↩